Glassy or amorphous alloys are of considerable technological interest owing to their unique physical properties as compared to the properties characterizing the polycrystalline forms of such alloys. In particular, cast products having a glassy structure, in the form of a filament or relatively thin elongated ribbon, have proven to be effective for winding into highly efficient cores for electrical transformers or other uses. Some recent developments in the casting of amorphous or glassy metal ribbons are reviewed in U.S. Pat. No. 4,332,848.
As is well known in the art, glassy alloys are rapidly quenched or cooled from a liquid state to a substantially amorphous solid state, typically having less than about 50% crystallinity. The quenching occurs at extreme cooling rates, namely, on the order to 10.sup.6 .degree.C./sec. The ribbon is typically formed by extruding the molten alloy from a pressurized reservoir through a restricted orifice of a nozzle onto a high speed cooling surface. The cast filaments are necessarily thin, owing to the extreme heat transfer requirement for preventing substantial crystallization.
It is necessary to wind the cast filament onto a storage wheel or reel in line with the casting apparatus for later processing into a transformer core or the like. The initiation of the in line winding process, however, is difficult since the casting speeds are so high, typically on the order of 1000-2000 meters per minute. Thus, the leading portion of the high speed filament must be captured on the fly as it departs the rapidly rotating cooling surface, then transferred and clamped to the take-up wheel and finally wound on the wheel. Exemplary prior arrangements of this type are shown in U.S. Pat. No. 4,116,394 to Smith et al and U.S. Pat. No. 4,239,187 to Boggs et al. As should be appreciated, the clamping must be accomplished quickly and precisely or an entangled mass of filament rapidly accumulates since the casting process is continuing throughout this operation at a rapid pace.
Heretofore, the gripping mechanism for clamping the filament to the storage wheel generally has taken the form of a pivotal filament gripping element mounted for rotation with the storage wheel (see Smith '394 patent). The gripping element includes a movable gripping lever formed with a gripping face and a cutting edge. The movable cutting edge cooperates with a stationary edge on the wheel. When actuated, the lever is designed to pivot and clamp the filament against the wheel. The two cutting edges are designed to cooperate and simultaneously cut the filament with the severed leader end of the filament being cast aside.
Disadvantageously, however, the Smith apparatus often fails to reliably provide the necessary gripping and cutting action to the filament. When the proper cutting action is not provided, the filament leader is pulled back onto the winding wheel to disrupt filament winding. In other instances, the cutting action may occur just prior to rather than simultaneously with, the clamping. When this occurs the filament slips free from between the gripping lever and the wheel, quickly becoming an entangled mass. Either of the above failures results in a costly shut-down of the casting operation and a clean-up operation. The reduced productivity with the forced shut-down of the casting operation has, in the past, been a significant hinderance in the commercialization of the amorphous metal casting process. Further, the unreliable cutting device is not easily corrected in Smith. Numerous attempts, such as, strengthening the spring action on the gripper, providing better alignment between the two cutting edges, and sharpening the cutting edges have all failed to increase the reliability. The metal ribbon by its nature is very tough and simply tends to spread the two cutting edges, thus trapping the ribbon between the edges without cutting. In other instances, the cutting action may precede the firm gripping action by a fraction of a second allowing the ribbon that is under substantial tension to be pulled loose and cause failure of the winding process. The increased complexity of the multiple part mechanism also increases the initial cost and the general maintenance requirements. Further, the gripping lever closing force provided by the spring fails to compensate for the different rotational forces acting to hold the gripping lever in the open position as the winding wheel rotates at different speeds. Thus, in this prior arrangement it is necessary to precisely time the release so that it occurs at exactly the same speed each time. Otherwise, the gripping lever tends to contact and grip the filament either too early or too late. This puts the contact point spaced away from the optimum position where the filament is laid in contact with the winding wheel by the transfer device. Under these circumstances, the clamping and cutting actions can malfunction leading to the need to abort the casting operation.
A need is therefore, identified for a clamping and cutting apparatus and method providing increased reliability in initiating the winding of a filament upon a rotating winding or storage wheel and cutting the leader.